Portability of computers or processors has brought a demand for increased memory storage capacity in small volumes. In an effort to meet this demand, small form factor disk drives have been installed in plug-in cassettes suited to such applications. Patent application Ser. No. 07/975,761, a related application, referenced above, is an example of such a disk drive application in a Personal Computer Memory Card International Association PCMCIA Type II cassette.
In a PCMCIA type of cassette application, there are four major areas requiring structural design attention.
1) The mechanical and electrical organizational relationship of the several parts within the cassette housing, including: PA1 2) The specific design of the disk assembly, including the disk motor, PA1 3) The specific design of the actuator assembly, usually a rotary actuator, including the actuator motor, and PA1 4) The integration of the disk drive parts with the memory cassette housing within the memory cassette housing.
a) the disk drive PA2 b) the disk controller PA2 c) the PCMCIA electrical connector, and PA2 d) any solid state memory advantageously placed in the cassette.
Such a disk drive application requires a low profile, hard disk assembly which necessarily includes the disk motor. Disk assemblies embodying features offering low profile design potential are seen in U.S. Pat. Nos. 5,195,002 and 5,251,082.
U.S. Pat. No. 5,195,002, to Sakurai, in one embodiment, discloses a disk assembly having a single disk mounted to the motor rotor of an axial gap, disk spindle motor. A rotary actuator assembly supports a transducer for movement to different radial locations with respect to a disk surface. A salient pole stator, having individual stator poles, is mounted beneath the motor rotor. The pole tips of the salient poles confront a surface of a permanent magnet ring which has permanent magnet poles. Positioning the salient pole stator and permanent magnet ring beneath the motor rotor, shields the head/disk assembly thereabove from stray fields of the motor. While this motor design, whether implemented in axial gap or radial gap configuration, is suited to low profile implementation, placing the salient pole stator beneath the motor rotor in an axial gap configuration, as shown, adds the stator thickness and the permanent magnet ring thickness to the profile dimension of the disk assembly.
Another design of memory disk assembly in a disk drive, is seen in FIG. 1 of the drawings of the present patent application. Here, the memory disk assembly 1 employs a radial gap disk spindle motor 2. A memory disk 4 is secured to the motor rotor 6 of the disk spindle motor 2. An actuator assembly 5 supports a magnetic head 5a for movement to different radial locations with respect to the memory disk 4. The motor rotor 6 is umbrella shaped and comprises a peripheral permanent magnet ring 8 having discrete permanent magnetic poles, which are radially magnetized and alternately poled in sequential circumferential positions around the permanent magnet ring 8. A salient pole stator 10 is mounted to a base 12a of a housing 12, beneath the motor rotor 6. The salient pole stator 10 has a plurality of salient poles 10a, different in number from the number of permanent magnet poles in the permanent magnet ring 8, each of which mounts a coil 10b. The pole tips 10c of the salient poles 10a confront an inner peripheral face 8a of the permanent magnet ring 8, defining radial gaps therebetween. The motor rotor 6 is of magnetic material and provides, in its peripheral rim, 6a, a flux return path for the permanent magnet poles of the permanent magnet ring 8. As in the case of the patent to Sakurai, the motor rotor 6 shields the head/disk assembly 4, 5, from the magnetic fields of the disk spindle motor 2. Likewise the profile dimension of the disk assembly 1 includes the salient pole stator.
U.S. Pat. No. 5,251,082 to Elliot et al provides a disk spindle motor for a disk assembly in which a salient pole stator is disposed in a position external to the motor rotor. The rotor of this disk spindle motor comprises a permanent magnet ring which has discrete circumferentially distributed permanent magnet poles. This permanent magnetic ring is secured to the periphery of a memory disk. The disk/ring assembly constitutes the disk motor rotor. The salient pole stator is disposed outside of the permanent magnet ring, at one side of the disk motor rotor, with the pole tips of the salient pole stator adjacent the permanent magnet rotor ring.
While Elliot et al provides some structural detail of their disk drive, little is said or illustrated with respect to the type of disk which is employed, with respect to specific structural aspects of attaching the permanent ring to the disk, with respect to disk warpage in mounting and supporting the permanent magnet ring, with respect to whether an axial or radial gap motor is used (FIG. 21 shows neither), with respect to containing the magnetic field of the disk spindle motor to obviate interference of the motor magnetic fields with the read/write function of the head/disk assembly or, with respect to the structural problems from gyrodynamic and centrifugal forces acting on the spinning disk(s), imposed by the permanent magnet ring on the periphery of each disk. Also, the problems associated with designing adequate motor magnetic circuits, including the permanent magnet ring on each disk for producing useful motor torque are not addressed.
A need exists for a low profile memory disk assembly having a disk spindle motor of improved performance.